This invention relates to MOS-gated semiconductor devices, and particularly to means for providing improvements in miniaturization of components of the devices and improvements in the electrical performance of the devices.
There now exists a relatively large number of different types of semiconductor devices all making use of metal-oxide-semiconductor (MOS) gate control structures. In general, such devices, e.g., small signal "complementary" MOS devices (CMOS) and power devices such as MOS field-effect transistors (MOSFET), insulated-gate-bipolar transistors (IGBT) and MOS controlled thyristors (MCT), make use of gate control structures comprising a metal electrode overlying a thin dielectric layer (the "oxide") on a surface of a semiconductor substrate including a channel region underlying the gate electrode and extending between source and drain regions of the gate control structure.
In all such devices, it is generally desirable to make the gate control structure as small as possible for maximum high density packing of the devices for high speed circuit operation. Even in power devices where generally large composite structures are required for power handling capacity, better electrical characteristics are obtained by making the gate control structure portions of the device as small as possible and connecting a large number of such gate control structures in parallel in the composite power device.
A presently preferred process for fabricating the various gate control structures includes the use of a masking layer and the photolithographic patterning of the mask for providing precisely dimensioned and positioned windows through the mask through which dopants are introduced into the underlying substrate. Present day limitations on how small and precise the gate control structures can be made are imposed by limitations in the precision with which certain dopants are disposed within the substrate. The present invention is directed at increasing the precision of at least one dopant introduction step whereby smaller and more precisely dimensioned devices can be made.